In a production liquid of an amide compound, particularly an amide compound obtained by hydration of a nitrile compound, impurities, such as a polymeric compound, a surfactant, a coloring component, an eluted component and the like, are generally present while the species thereof are different depending on the production process thereof. In order to remove them, for example, a purification process using activated carbon is described in JP-A-61-115495 and JP-A-61-122253 (EP-A-182578), a purification process using an ion exchange membrane is disclosed in JP-A-61-115058, and a purification process by a porous hollow fiber film is disclosed in JP-A-61-122227 (EP-A-188068).
However, the purification processes using an ion exchange membrane and a porous hollow fiber film cannot avoid economical demerits upon practice, such as necessity of a special purification equipment and the like.
In the purification process using activated carbon, while no special equipment is required, impurities are still present in the resulting product, and the process is insufficient from the standpoint of efficiency. Particularly, in the case where an amide compound is produced by directly hydrating a nitrile compound by using a nitrile hydratase, which is an enzyme having an ability of hydrating a nitrile, or the like, protein originated from microorganisms mixed in the reaction solution is insufficiently removed by the purification process by activated carbon according to the conventional technique, and as a result, the reaction solution is liable to be foamed when it is a trace amount, or the reaction solution becomes clouded when the amount is large, whereby the quality of the product is adversely affected.
Therefore, an object of the invention is to provide a process for effectively removing impurities contained in a solution containing an amide compound. More specifically, an object of the invention is to provide a simple and effective purification process in the case where an amide compound-containing solution obtained upon producing a corresponding amide compound from a nitrile compound is processed with activated carbon.